Adlib OPL-2/OPL-3 Yamaha FM synthesizer support.

Supports:
  Adlib FM synthesizer @ 0x388
  Sound Blaster FM synth (OPL-2 or OPL-3) @ 0x388

ISA PnP notice: If you have a Sound Blaster 16 PnP installed and this
program is unable to see the OPL-2/3 synth at 0x388, use the PNPCFG
utility in the SNDSB Sound Blaster library to assign resources to the
card. Make sure you assign the OPL port to 0x388.

TODO: This code does not yet support multiple OPL chips, or OPL chips
residing at an address other than 0x388.

